Adenovirus infection of permissive human cells leads to severe inhibition of both translation of cellular mRNAs and appearance in the cytoplasm of newly-synthesized cellular mRNAs. The mechanisms by which cellular biosynthetic systems are subverted by the virus operate post- transcriptionally, and are mediated by specific viral gene products. Adenovirus-infected cells thus serve as valuable model systems in which to investigate post-transcriptional mechanisms that regulate eukaryotic gene expression. Selective export of viral, late mRNAs from the nucleus requires the viral, early E1B 55kD and E4 34kD proteins. The molecular functions of these viral early proteins are not, however, well understood. An important goal of this proposal is to remedy this situation, by careful investigation of the properties of transcription units that determine selective export of their processed transcripts in adenovirus-infected cells. These studies will exploit reporter genes under the control of a steroid hormone- inducible enhancer-promoter to determine whether transcriptional activation per se or residence of a transcription unit in the viral genome are necessary and sufficient for selective export. Subsequently, examination of the intranuclear organization of specific RNAs when they can and when they cannot be exported will be used, in conjunction with mutational analyses of the E1B and E4 proteins and experiments to identify the molecular signals specifying export, to develop and test models that can account for the export selectivity characteristic of adenovirus- infected cells. These studies should improve our understanding of an important adenoviral regulatory mechanism, as well as a key, but poorly understood, step in production of eukaryotic mRNA, one that is also targeted by other viruses, including human immunodeficiency virus. We have previously established that efficient initiation of translation of all viral, late mRNAs requires the L4 100kD non-structural protein. Although this protein possesses RNA-binding activity that correlates with its translational function, no evidence that it binds specifically to viral, late mRNAs has been obtained. Thus, the L4 100kD protein can be distinguished from other regulators of translation of specific eukaryotic mRNAs. We will determine whether the viral, late mRNAs are recognized by the L4 100kD protein by virtue of their selective export from the nucleus during the late phase of infection. The intracellular location and metabolism of this protein will also be examined, to permit specific mechanisms by which it might stimulate translation to be identified and tested.